Inherently slow growth in two Caribbean epiphytic species: A demographic approach

In relation to the drought-prone and nutrient-poor habitat, vascular epiphytes are routinely referred to as inherently slow-growing plants, although actual evidence is rare. To test this notion we measured in situ growth of the understorey orchid Aspasia principissa and the tank bromeliad Vriesea sanguinolenta, and, for the latter species, also the growth under favourable conditions in the greenhouse. Using growth analysis we show: (1) that in an intraspecific comparison, small to intermediate individuals yield the highest relative growth rates (RGR) in situ: A. principissa: 1.6 10−3 d−1; V. sanguinolenta: 3.3 10−3 d−1; (2) that the bromeliad reaches maximum size after ca. 15 yr, while the orchid needs at least 20 yr; and (3) small V. sanguinolenta plants exhibit a highly plastic growth response to favourable conditions in the greenhouse, reaching an almost 10-fold increase in RGR. In spite of a substantial increase in growth under more favourable conditions, our results are consistent with the notion that epiphytes are inherently slow growing organisms. Nomenclature: D'Arcy (1987). Abbreviations: DM = Dry mass; LL = Length of the longest leaf of a plant; PPFD = Photosynthetic photon flux density; PsbL = Length of the most recent pseudobulb; RGR = Relative growth rate; SC = Size category.